Life history characteristics, harvest data, population trends and conservation statuses of huntable waterbirds in the UK.

Wintering bird populations for the UK were obtained from the latest published estimates (Frost et al. 2019). The estimate for mallard was increased by 2.6 million birds to account for the annual release of captive-raised birds for shooting purposes (Madden 2021). We estimated a standard deviation for the population estimates by averaging the Wetland Bird Survey (WeBS; Frost et al. 2021) index for each species for the winters 2012/13 – 2016/17, which corresponded to the period used to estimate duck populations. We treated this mean index as equal to the estimate from Frost et al. (2019) and then calculated population estimates for each year based on their WeBS indices and calculated the standard deviation of these estimates. Population estimates for greylag goose, pink-footed goose, golden plover, snipe and woodcock were based on single years, but the same time frame was applied to standard deviation estimates in order to account for any interannual differences. The latest (2016) harvest estimates and 95% confidence intervals were taken from Aebischer (2019). Species specific body mass was taken from Robinson (2005). Where sex-specific body mass was reported we averaged male and female masses.

We modelled the resident and migratory populations of greylag geese and woodcock separately. The resident woodcock population was estimated as three times the number of breeding males. This was subtracted from the total estimated overwintering woodcock population to provide an estimate of the migratory woodcock population. Resident woodcock harvest was estimated as equal to the proportion of breeding birds in the overwinter population (13%) The remaining 87% of total harvest was assigned to migratory woodcock. We recognise that further mortality of UK breeding woodcock will occur outside the UK in southern Europe, but we have no estimate of this mortality and can only consider the contribution of UK hunters to the harvest of birds that winter in the UK in this initial assessment. Population estimates for Icelandic and British greylag geese overwintering in the UK are reported separately and no adjustment is needed. An estimated harvest of migratory Icelandic greylag geese in the UK (Frederiksen 2002) was deducted from the total UK greylag goose harvest to provide an estimate of the harvest of British greylag geese. However, it should be noted that the estimate was from 1996-2000 and no new estimates have been made. 

Short-term (2008-2018) and long-term (1970-2018) wintering population trends were taken from Burns et al. (2020), except for common snipe and Eurasian woodcock. Common snipe trends were taken from Woodward et al. (2020), with caution advised due to the small sample size. Resident woodcock long-term and short-term population trends were estimated at -29% for both on the basis of reported declines in breeding woodcock (Balmer et al. 2013; Heward et al. 2015). Migratory woodcock short-term and long-term trends were estimated at -11% and -22% on the basis of a 4-18% decline from 2008-2018 and an 11-33% decline from 1980-2018 (BirdLife International 2021). Bird population status in the UK (Red/Amber/Green) was taken from Birds of Conservation Concern 5 (BoCC5; Stanbury et al. 2021).

Estimates of adult survival were taken from Robinson (2005) with reported standard errors multiplied by 1.96 to give an approximate 95% confidence interval. The average standard error for all reported waterbirds (0.03) was used for species when no standard error was reported (e.g. wigeon, shoveler, greylag goose, woodcock and golden plover). We used the same survival estimates for both resident and migratory populations of woodcock and greylag geese. These adult survival estimates include mortality from hunting and so are likely to underestimate the maximum achievable survival rates under optimal conditions and so survival was also estimated using species mass. Age at first reproduction (alpha) was also taken from Robinson (2005).